Lifting a granular box by a half-buried rod

TL;DR

This paper investigates how a half-buried rod can lift a container of granules by analyzing frictional forces, stress distribution, and the conditions for successful lift-off, combining theoretical, experimental, and visual methods.

Contribution

It introduces an analytic expression for the critical depth for lift-off and demonstrates the role of friction direction change and stick-slip phenomena in granular lifting.

Findings

Derived the critical depth formula for lift-off.

Confirmed friction force direction change via photoelasticity.

Identified stick-slip behavior during failed lifts.

Abstract

We studied an interesting experiment that showed a half-buried chopstick lifting a full bottle of granules off the table. In Janssen theory, the friction force provided by the container wall helps alleviate the weight of the granules. How can a thin rod with a much less contact area support the full weight plus that of the container? Insights are gained by allowing the friction on the wall to change direction before solving the Janssen equation. We obtained the analytic expression for the critical depth of granules that enables a successful lift off. In addition, we established that the stick and slip phenomenon exists during a failed lift off by analyzing the frequency of fluctuations in the pull force. Finally, a photoelasticity experiment was employed to directly visualize the stress field sensitive to the pull force, and verify the directional change of friction force from the wall.